1. Field of the Invention
The present invention relates to a keyboard device and particularly to a keyboard body positioning and fixing structure in a keyboard device having a keyboard body and a case which accommodates the keyboard body therein.
2. Description of the Related Art
A conventional keyboard generally has a keyboard body with a large number of key tops attached thereto and a case which accommodates and holds the keyboard body therein. The case is of a combined structure comprising an upper case which covers the upper surface side of the keyboard body and a lower case which covers the lower surface side of the keyboard body, the upper case having window portions through which a large number of key tops are exposed. The reason for adopting this structure is that this structure facilitates the keyboard assembling work. The keyboard body has several kinds of key groups different in function, including ordinary types of input keys, ten keys, and function keys. The key groups are partitioned and somewhat spaced from one another by beam portions each disposed between adjacent window portions formed in the upper case.
Recently, in the field of information processors such as personal computers, there has been an increasing demand for the reduction of size, thickness and weight from the standpoint of space saving and portability improvement. With such a demand as background, also in the field of keyboard as an input device of an information processor, a demand has been being raised to the effect that the keyboard itself should be reduced in size, thickness and weight. In this connection, for reducing the size of conventional keyboards having the above structure, there has been proposed a keyboard in which the number of beam portions for partitioning key groups is decreased, the spacing between adjacent key groups is made smaller, and the width of an outer frame portion is reduced. According to this keyboard, the reduction in size of the keyboard can be implemented in comparison with the other conventional keyboards of the foregoing structure because the key group-to-key group spacing is narrowed and the external frame is reduced in width. Further, the reduction in weight of the keyboard can be attained by using a light-weight resin as the material of the case.
However, although the reduction in size and weight of the keyboard can be attained by making some improvement with respect to the structure and material, other inconveniences have occurred.
For example, at the time of installing the keyboard body into the case, it is necessary to effect positioning of the keyboard body accurately with respect to the case. But, since there is no beam portion crossing above the keyboard body, the positioning of the keyboard body relative to the case is inevitably performed along an edge portion of the keyboard body. In this type of a conventional keyboard, such a positioning is conducted at an end portion of an edge extending in the longitudinal direction of the keyboard body. In such a positioning method, it has been difficult to attain a satisfactory positioning accuracy particularly at the opposite-side end portion. Usually, therefore, a slight clearance is formed between window edges in the upper case and the key tops located on the outermost periphery so as to prevent mutual contact. However, there has been the problem that the clearance is not uniform throughout the whole of the keyboard. Such a problem may be avoided by providing positioning portions at both ends, but in this case an extra space is required for such positioning portions.
The keyboard body is fixed to the lower case with screws or the like from the back side of the lower case so as not to be visible in the normal state of use. No matter how simplified the structure of the case may be for the reduction in size and weight of the keyboard, the case and the keyboard body must not become easily disengaged from each other at their fixed portions when a slight shock is exerted on the keyboard. It is necessary that the keyboard body be held and fixed positively at a predetermined position in the case.